Erectile dysfunction is the inability to obtain and maintain a penile erection sufficient for sexual intercourse or other sexual expression. A number of factors can place an individual at risk for this disorder, for example, trauma, pelvic surgery, hypercholesterolemia, ischemic heart disease, peripheral vascular disease, chronic renal failure, diabetes, the use of certain medicaments including some types of antihypertensive agents, digoxin, or the excessive use of narcotics, alcohol, tobacco, etc. Methods for treating erectile dysfunction include the use of vacuum devices and penile implants, as well as the administration of medicaments such as yohimbine, papaverine and apomorphine. Improved methods for treating this disorder are sought, however, as the aforementioned methods do not provide sufficient efficacy and/or are accompanied by drawbacks or side effects such as erosion, pain, priapism, or gastrointestinal discomfort.
A penile erection is dependent upon the presence of adequate levels of cyclic guanosine 3′,5′-monophosphate (cGMP), especially in corpora cavernosa tissue. Thus, administering an inhibitor of a cGMP phosphodiesterase (cGMP PDE), particularly a selective inhibitor of cGMP PDE Type 5 (PDE 5), provides a means for achieving and maintaining an erection and therefore, for treating erectile dysfunction. See Trigo-Rocha et al., “Nitric Oxide and cGMP: Mediators of Pelvic Nerve-Stimulated Erection in Dogs,” Am. J. Physiol., Vol. 264 (February 1993); Bowman et al., “Cyclic GMP Mediates Neurogenic Relaxation in the Bovine Retractor Penis Muscle,” Br. J. Pharmac., 81, 665-674 (1984); and Rajfer et al., “Nitric Oxide as a Mediator of Relaxation of the Corpus Cavernosum in Response to Nonadrenergic, Noncholinergic Neurotransmission,” New England J. Med., 326, 2, 90-94 (January 1992). Sildenafil, for example, has been described as a PDE 5 inhibitor useful for treating erectile dysfunction. See Drugs of the Future, 22, 138-143 (1997).
Recent examples of other compounds claimed as PDE 5 inhibitors include fused pyridazine compounds (WO 96/05176 and U.S. patent application Ser. No. 09/393,833), anthranilic acid derivatives (U.S. Pat. No. 5,716,993), fused pyridopyridazine compounds (U.S. patent application Ser. No. 09/526,162), and quinazolinone compounds (U.S. Pat. No. 6,087,368). The present invention provides compounds that are potent and selective inhibitors of cGMP PDE 5. These compounds may be employed in treating erectile dysfunction. In view of their activity, these compounds can also be used in treating other disorders responding to the inhibition of cGMP PDE, such as various cardiovascular disorders.